The present invention relates to a manually operated hammer drill.
A manually operated hammer drill usually includes a spindle which drives a chuck about an axis of rotation during drilling operations. The spindle itself is usually driven by an electric motor. Typically, such a hammer drill also includes a pneumatic hammer mechanism, which exerts a hammering action on the tool inserted in the chuck during hammer drilling operations. A hammer mechanism of such kind typically includes a piston, which in hammer mode moves back and forth parallel to the axis of rotation inside a cylinder formed in the spindle. The reciprocating movements of the piston are intended to create pulses of pressure inside the cylinder that cause an actuation piston to move back and forth as well, so that it strikes a percussion piston which in turn transfers these impacts to the respective tool. In order to be able to create these pressure pulses as effectively as possible, it is expedient to seal the piston off from the cylinder. For this purpose, the piston may be equipped with at least one radial groove in which an annular seal is disposed. This annular seal is prone to very rapid wear because of the reciprocating motion of the piston.
Modern hammer drills may also be equipped with a hammer action deactivation switch, which enables drilling to be performed without percussive action. To do this, for example, a powertrain between the spindle and the driving electric motor is interrupted, for example by means of a coupling or similar. When hammer mode is switched off, the piston does not execute any reciprocating movements in the cylinder. In drilling mode, the spindle rotates about the axis of rotation and thus also about the piston. When hammer mode is deactivated, this subjects the annular seal to particularly high stress. As a result, it may overheat and be damaged. A damaged annular seal reduces the sealing effect between the piston and the cylinder which in turn impairs the effectiveness of the pressure pulses in hammer mode and thus also the performance of the hammer drill.